(a) Technical Field of the Invention
The present invention generally relates to a novel bidirectional output mixed hydraulic power system, and more particularly to one that prevents the switching of direction unsmooth due to pressure accumulation in the fluid passage in bidirectional dual power output and thus achieving an effect of bidirectional hydraulic pressure and mixed dual power hydraulic output.
(b) Description of the Prior Art
A conventional hydraulic power output system (shown in FIG. 3) comprises a mechanical hydraulic pump 70, an electrical hydraulic pump 71, a pressure relief valve 72, a check valve 73, and a fluid tank 74. The mechanical hydraulic pump 70 receives manual power as the operation power to draw in, pressurize, and output a hydraulic fluid. The electrical hydraulic pump 71 receives operation power from an electrical motor to draw in, pressurize, and output the hydraulic fluid (output in a single direction). The pressure relief valve 72 functions for relief of pressure when the pressure exceeds a predetermined level. The check valve 73 prevents a returning or reversing flow of the hydraulic fluid. The fluid tank 74 stores and supplies the hydraulic fluid to the pumps so that when the hydraulic power output system is put in operation, outlets of both the mechanical hydraulic pump 70 and the electrical hydraulic pump 71 are provided with check valves 73 to prevent, during the operation of one of the pumps, the hydraulic fluid from flowing reversely in the other one of the pumps so as to achieve mixed power hydraulic output with the two pumps. A drawback is that the mechanical hydraulic pump 70 and the electrical hydraulic pump 71 both have unidirectional hydraulic output, making it not possible to carry out bidirectional hydraulic output.
Another known hydraulic power output system (shown in FIG. 4) comprises a dual pressure valve 80, an electrical hydraulic pump 81, pressure relief valves 82, check valves 83, and a fluid tank 84. When the hydraulic power output system is put in operation, similar to the unidirectional mode of mixed power output, an outlet of the electrical hydraulic pump 81 is operated in combination with the check valve 83 to carry out mixed output of dual powers, which induces pressurization in a first direction. Since the hydraulic fluid is present in the check valve 83, expansion of fluid piping and accumulation of pressure may result and the hydraulic pressure would be kept and accumulated in the fluid piping, making the dual pressure valve 80 of the fluid returning passage pushed rightward, making the pressurization direction changed to pressurization in a second direction, thereby keeping the dual pressure valve 80 normally in an open condition for the fluid returning passage in the second direction. This makes the hydraulic pressure directly return, through the right-side fluid returning passage, back to the fluid tank 84, being unable to achieve pressurization and leading to pressure accumulation to make it impossible to change direction for driving.